1. Field of the Invention
The present invention relates to a clinical thermometer for calculating a prediction value of an equilibrium temperature on the basis of a temperature of a portion of body to be measured.
2. Description of the Prior Art
A conventional electronic clinical thermometer capable of calculating a prediction value is disclosed, e.g. in U.S. Pat. No. 4,629,336, which will be described below with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram showing a basic arrangement of a conventional electronic clinical thermometer for calculating a prediction value. The electronic clinical thermometer capable of prediction is basically constituted by a temperature detection section 1, an operation section 2 including a parameter selector 16, and a display section 3. The temperature detection section 1 includes a sensor such as a thermistor and serves as a circuit for detecting a temperature of a portion to be measured in a real-time manner. The operation section 2 calculates an equilibrium temperature in response to a temperature signal from the temperature detection section 1 when predetermined conditions are satisfied, and outputs the resultant value to the display section 3 as a statistical prediction equilibrium temperature (to be referred to as a prediction value hereinafter). The parameter selector 16 serves as a circuit for feeding back an operation result of the prediction value to select coefficient parameters (to be referred to as parameters hereinafter) of an equation for providing a more accurate prediction value.
FIG. 2 is a block diagram showing a detailed arrangement of the conventional electronic clinical thermometer capable of prediction.
The temperature detection section 1 is constituted by a sensor 5 such as a thermistor and a temperature detector 6. The temperature detector 6 detects an electrical signal from which the sensor 5 outputs in response to a temperature of a portion to be measured, and intermittently outputs temperature data 21 and 22 corresponding to the detected electrical signal to the operation section 2.
The operation section 2 comprises a measurement control circuit 7, a time measuring circuit 8, a temperature memory circuit 9, a prediction value calculator 10, a prediction value monitor circuit 15, and the parameter selector 16. The measurement control circuit 7 receives a temperature data signal 21 from the temperature detector 6, always monitors the temperature of the portion to be measured in a real-time manner, and outputs a prediction start signal 24 to the time measuring circuit 8 when the temperature data satisfies predetermined conditions. At the same time, the measurement control circuit 7 keeps outputting operation command signals 23 to the prediction value calculator 10 in synchronism with the temperature data signals 21 intermittently supplied from the temperature detector 6 until the predetermined conditions are satisfied. The time measuring circuit 8 starts counting time at the same time when the temperature detector 6 outputs the temperature data signal after a power switch of the electronic clinical thermometer is turned on and the circuit is energized. When the time measuring circuit 8 receives the prediction start signal 24 from the measurement control circuit 7, time data thus obtained is reset and counting of time is restarted. This time data is output to the prediction value calculator 10 as elapsed time data 25. The temperature memory circuit 9 serves as a circuit for temporarily storing the temperature data 22 in accordance with a predetermined rule when the temperature data 22 from the temperature detector 6 is input to the temperature memory circuit 9, and outputs the stored data to the prediction value calculator 10 as needed. The prediction value calculator 10 is programmed with a functional equation for obtaining a prediction value as a function of an elapsed time and a temperature by using several parameters which affect a calculation of the prediction value of an equilibrium temperature. In an initial state, i.e., when the operation command signal 23 from the measurement control circuit 7 is input to the prediction value calculator 10 at the first time, the parameters are reset and predetermined values are set. The prediction value calculator 10 calculates a prediction value according to the above equation, in which the parameters are set, using temperature data 26 from the temperature memory circuit 9 and the elapsed time data 25 from the time measuring circuit 8. The prediction value calculator 10 outputs the resultant data to the prediction value monitor circuit 15 as prediction value data 30. The prediction value monitor circuit 15 always monitors the prediction value data 30 periodically input thereto. When a change in prediction value as a function of time, e.g., falls within a given range for a predetermined period of time, the prediction value monitor circuit 15 determines that the result of the prediction value calculated by the prediction value calculator 10 is correct, i.e., that selection of the parameters which determine the functional equation is correct, thereby outputting a prediction value signal 33 to the display section 3. When the prediction value exceeds the given range within the predetermined period of time, a negative-feedback control signal 32 is output to the parameter selector 16 together with the prediction value 33. The parameter selector 16 receives the negative-feedback control signal 32 and updates the parameters which affect the calculation of the prediction value. More specifically, the parameter selector 16 selects parameter values for reducing the change in prediction value for the predetermined time from several preset values. Thereafter, the updated parameter data is output to the prediction value calculator 10 as an electrical signal 31. The prediction value calculator 10 receives the electrical signal 31, and then receives the operation command signal 23 from the measurement control circuit 7 again, so that the prediction value calculator 10 calculates a prediction value in accordance with the elapsed time data signal 25 from the tim measuring circuit 8 and the temperature data 26 from the temperature memory circuit 9 on the basis of the updated parameters. A prediction value thus calculated is output as the prediction value data 30 again, and monitored by the prediction value monitor circuit 15. The above-described process is repeated in the prediction value monitor circuit 15. As a result, the prediction value is displayed on the display section 3 while the prediction value is continuously updated.
The above description will be explained with reference to characteristic graphs shown in FIGS. 3 and 4. In FIG. 4, reference symbol T(t) denotes an actual body temperature rise curve, which is plotted as a continuous curve based on temperature data detected and intermittently output by the temperature detector 6. Points T(t.sub.0), T(t.sub.1), . . . on T(t) represent temperatures at elapsed times t.sub.0, t.sub.1, . . . , respectively. Reference symbol W(t) denotes a line which is plotted to show a continuous change in prediction value displayed on the display section 3 as a function of the lapse of time. Since the parameters of the equation for calculating the prediction value are changed, and the prediction value is corrected, the line W(t) is plotted stepwisely as a whole. Reference symbols W(t.sub.0), W(t.sub.1), . . . denote the corrected prediction values at elapsed times t.sub.0, t.sub.1, . . . In addition, reference symbol T(t.sub.n) denotes an actual equilibrium temperature at elapsed time T.sub.n.
A method of calculating a prediction value in the prediction value calculator 10 will be described below. The prediction value W(t) of an equilibrium temperature is expressed by the following equation. EQU W(t)=T(t)+V(t)
V(t) is a so-called correction value as a function of elapsed time t, and is solely determined by a value of a parameter C. For example, in FIG. 3, a plurality of curves indicated by narrow broken lines, which represent an equation V(t) for obtaining correction values when the value of the parameter C is C.sub.0, C.sub.1, . . . The plurality of curves are required for V(t) to cope with variations in body temperature rise curves due to personal differences or different measuring conditions. Accordingly, an appropriate correction value V(t) can be selected by updating the value of the parameter C. The parameter C is updated at the elapsed times t.sub.0, t.sub.1, . . . and V(t.sub.0), V(t.sub.1),. . . are correction values after the parameter C is updated.
When the power source is turned on and an entire circuit shown in FIG. 6 is operated, the temperature detector 6 converts electrical signals output from the sensor 5 in response to an ambient temperature into corresponding temperature data at predetermined intervals of time, e.g., every two seconds, and outputs them as the temperature signals 21 and 22. The measurement control circuit 7 always monitors the temperature data signal 21 input thereto, and outputs the prediction start signal 24 and the operation command signal 23 when the temperature data satisfies a predetermined condition. In this case, however, the conditions are not satisfied, and hence the signals are not output. The predetermined condition means, e.g., that 10 seconds have elapsed after the temperature exceeds 30.degree. C. and rises at a rate of 0.1.degree. C./sec.
The time measuring circuit 8 starts counting elapsed time immediately after the power switch is turned on, and the temperature memory circuit 9 stores the temperature data each time the temperature data signal 22 is input thereto according to the predetermined rule. In this state, when the sensor 5 is inserted in a portion to be measured, the value of the temperature data is increased along a curve T(t) plotted in FIG. 8. When the temperature data satisfies the predetermined condition (10 seconds have elapsed after the temperature exceeds 30.degree. C. and rises at a rate of 0.1.degree. C./sec) at time t.sub.0, the predicton value calculator 10 starts operation after the parameter C of the equation for providing the prediction value is reset by receiving the operation command signal 23 from the measurement control circuit 7.
The time measuring circuit 8 is reset by receiving the prediction start signal 24, and restarts counting an elapsed time. In this case, elapsed time is t.sub.0. When operation is started at elapsed time t.sub.0, the parameter C is reset to be a value of an equation for providing a prediction value of an equilibrium temperature corresponding to an average body temperature rise curve from the statistical point of view. In this case, the value is given as C.sub.0. The above correction value V(t) whose value of the parameter C is C.sub.0 can be represented by a curve indicated by a broken line of C=C.sub.0 in FIG. 3.
As an operation result, the correction value is given as V(t.sub.0) when the parameter C is C.sub.0 and the elapsed time data is t.sub.0. In this case, the prediction value W(t.sub.0) is obtained from current temperature data T(t.sub.0) as follows: EQU W(t.sub.0)=T(t.sub.0)+V(t.sub.0)
and is output from the prediction value calculator 10 as a prediction value data 30. Thereafter, a curve corresponding to the function V(t) for obtaining a correction value, in which C=C.sub.1, is plotted. In synchronism with sampling of the temperature at predetermined time intervals, e.g., every two seconds, the prediction value calculator 10 calculates prediction values according to the above equation using the corresponding elapsed time data signals 25 and the corresponding temperature data 26 and outputs the resultant values to the display section 3 through the prediction value monitor circuit 15. As a result, the value corresponding to the curve W(t) showing the prediction value between elapsed times t.sub.0 and t.sub.1 in FIG. 4 is displayed as a numerical value.
The prediction value monitor circuit 15 always monitors a change value .vertline.dW(t)/dt.vertline. of the prediction value as a function of time. When the change amount exceeds a predetermined value, e.g., a (.vertline.dW(t)/dt.vertline.&gt;a) continues within a given period of time, the prediction value monitor circuit 15 outputs the negative feedback control signal 32 so that a new parameter C is selected by the parameter selector 16 and is output to the prediction value calculator 10 as the electrical signal 31. When the above condition (.vertline.dW(t)/dt.vertline.&gt;a) is satisfied at elapsed time t.sub.1 in FIG. 4, the parameter C is updated to a new value C.sub.1, and hence the equation V(t) for obtaining a correction value is represented by a curve of C=C.sub.1. A prediction value W(t.sub.1) at elapsed time t.sub.1 can be expressed using corresponding temperature data T(t.sub.1) and a corresponding correction value V(t.sub.1) as follows: EQU W(t.sub.1)=T(t.sub.1)+V(t.sub.1)
A parameter is selected by the parameter selector 16 by the following method. The parameter selector 16 selects an appropriate curve V(t) for providing a correction value with respect to a body temperature rise curve depending on cases, i.e., dW(t)/dt&gt;a or dW(t)/dt&lt;-a (a is a positive number), and changes the parameter C in a direction where dW(t)/dt is decreased. For example, since dW(t)/dt&lt;-a in FIG. 8, the value C.sub.1 of the parameter C is selected such that C.sub.1 &lt;C.sub.0. In practice, the value C.sub.1 is given by subtracting a predetermined value from the value C.sub.0, e.g. C.sub.1 =C.sub.0 -1. Subsequently, the parameter C can be given in the same manner as described above. In general, EQU C.sub.n =C.sub.n-1 1
where n is an integer. The predetermined value is not limited to 1, but can be changed with the lapse of time.
After the value of the parameter C is selected at elapsed time t.sub.1 and the value C.sub.0 is replaced with the value C.sub.1, the function V(t) for providing a correction value is changed with the lapse of time as shown by the curve C=C.sub.1 in FIG. 7, and hence the numeral value corresponding to the curve of the prediction value W(t) between elapsed times t.sub.1 and t.sub.2 is output to the display section 3. Thereafter, a loop (negative-feedback operation) constituted by the prediction value calculator 10, prediction value monitor circuit 15, and the parameter selector 16 continues in a similar process. During that time, the value of the parameter C is updated to C.sub.2, C.sub.3, and C.sub.4 at elapsed times t.sub.2, t.sub.3, and t.sub.4, respectively. As a result, the prediction values W(t) are successively output to the display section 3 as values plotted as a curve shown in FIG. 4.
After the value of the parameter C is changed to a value C.sub.4 at elapsed time t.sub.4, if the change amount of the prediction value W(t) after a predetermined period of time falls within the predetermined range, i.e., .vertline.dW(t)/dt.vertline.&lt;a (a is a value of the predetermined value), the prediction value monitor circuit 15 determines that the equation V(t) for providing a correction value is optimal for a body temperature rise curve currently measured and informs a user of the current decision as an optimal decision by a buzzer or the like.
In FIG. 2 illustrating the conventional example, the process wherein a prediction value is calculated in the prediction value calculator 10, monitored in the prediction value monitor circuit 15, and negatively fed back to the parameter selector 16 is made to improve adaptive precision of an equation corresponding to an actual body temperature rise curve by selecting a new parameter of the functional equation to be operated depending on a change in prediction value, which is an operation result, as a function of time and by feeding back the resultant value, thereby obtaining an accurate prediction value.
However, as is apparent from FIG. 4, since each parameter for determining the equation to be operated is selected step by step according to a predetermined order and sequentially changed, a certain number of updating cycles is required to select an optimal parameter.
As is apparent from FIG. 3, according to the conventional example, only one parameter determines an equation to be operated. Therefore, even if a an equation is arranged to be exclusively used for a body portion to be measured, e.g., the mouth or an armpit, since only one parameter is selected from a predetermined value, an optimal value is not necessarily obtained, thereby degrading selection of the parameter. More specifically, since a number of equations obtained by selecting a given number of parameters from the predetermined number of parameters is limited, variations in temperature curve due to personal differences and different measuring states cannot be sufficiently coped with, thereby posing a problem in terms of accurate measurement.
As has been described above, in the conventional electronic clinical thermometer capable of predicting values, the advantages obtained by means of prediction have not been sufficiently utilized.